Efficiency Definition and 901 Threads

Homework Statement I've attached the question Homework Equations The problem is I don't know what equation(s) I have to use. The Attempt at a Solution This question my part of my thermofluid dynamics course but I cannot find a formula in my textbook that uses an irradiance...

Hi, I'm new to working with gratings. From using the basic grating eqn., I'm able to model the diffraction angles for each order with different angles of incidence upon the grating and I can calculate the dispersion given a broadband source with known minimum and maximum wavelength...

Homework Statement The cost of fuel to propel a boat through the water (in dollars per hour) is proportional to the cube of the speed v. A certain ferry boat uses $100 worth of fuel per hour when cruising at 10 miles per hour. Apart from fuel, the cost of running this ferry (labor...

I know a guy that is really big into hot rods. He's got a late 80's model firebird with a custom engine in it. Dudes got probably got between $15-20k in the engine alone. It puts out somewhere just over 1000 hp, and he's done all the work on his own, so I feel inclined to believe the guy. But I...

Hi there, I'm reading a report about the efficiency of the drive train of an electric car. The author recorded the speed and acceleration of the car over a period of time and created the graph below to illustrate the efficiency. Could anybody tell me what the relationship is between the...

Hello everyone, Long time follower, first time user here. I have got a Q about propulsive efficiency. My understanding of the jet engine in a nutshell is that air is compressed in the compressor (pressure and temp go up), energy added in the combustor (large increase in temp), work...

Hello, I am looking for research results, report etc. dealing with -aerodynamic efficiency and static longitudinal stability- Couldn´t find anything useful yet! Any ideas would be very much appreciated. Best Regards, granby

Homework Statement Muscles operate with an efficiency of about 18.0 percent in converting stored chemical energy into work. How much chemical energy will be expended by a 63.6 kg person in the process of ascending several flights of stairs to a height of 21.0m? Homework Equations pe=...

Question is attached Thanks!

Hi. I'm doing research relating to solar cells and came about the topic related to effective masses. The wiki article stated how effective mass (solid state materials) influences the efficiency of solar cells, but doing more research I couldn't find any solid examples of an effective mass vs...

Is it strictly true that an engine will be more efficient if operating in a hotter environment... e.g. your car is more efficient in the summer than the winter? Just going through thermo 1, not a HW question, but it just seems to be true to me because the simple Newton's law of cooling says...

Homework Statement Hi, VERY URGENT and I am so confused Find the efficiency of the optimum trebuchet. Optimum trebuchet Specs: Counterweight= 5kg Sling Length= 78cm (laid out fully) Length from fulcrum to load= 44cm Length from fulcrum to counterweight=16cm Height the weight drops...

I understand a changing current in a wire gives way to an opposite magnetic field that resists the induced magnetic field, until there is no change in magnetic field, then you're left with a constant induced magnetic field. So my confusion with the antenna is when an electron rapidly...

So the current estimate is that an ICE engine is about 20%. If we were able to increase the efficiency of a given engine, would that result in a proportional decrease in exhaust temperatures? (Given that driveline loss to friction is constant)

Thank you Regards

I am currently using a 600HP DC motor for an extruder application and I am exploring the idea of switching to a 600HP AC motor. What kind of energy savings/efficiency can I expect if any?

Homework Statement The energy lost operating a low-speed chairlift is the same as the energy lost operating a high-speed lift of equal path length. What happens to the efficiency when you change from a low speed to a high speed chairlift? Homework Equations We know that high speed...

If we look at wind turbines used for power generation, they typically have 3 blades, and the blades are very slender compared to the blades of a house fan. I don't understand how such a slender blade can capture a significant amount of the wind's energy. The energy available in the wind is...

What affect does the temperature of a solar panel have on it's efficiency? I know they become less efficient at higher temperatures, but is this effect linear? Would decreasing the temperature sub-freezing temperatures do anything? On a related note, apparently they have invented a transparent...

I've recently gained an interest in solar cells and it's development. I know the basic working principle of solar cells, but other than that I'm quite clueless about the field. I was wondering, what is the process of increasing solar cell efficiency like? Are there analytical ways of...

Hello, I would like to know if the motor efficiency is changing with respect to applied voltage or it doesn't change. What I do mean. The efficiency=(V*I)/(Torque*velocity) and the power losses= I^2*R. Can I say that mechanical power ( Torque*speed)=V*I-I^2*R If so, can I say that the...

To understand, in a specific case, which motion spends less energy - angular or linear - I want to ask an unusual question. Which kind of door - hinged or sliding door - needs less energy to change its state from closed to fully opened, in a specific interval of time "t"? If I want to close...

Heya, id like a little help calculating the efficiency of some steam heat exchangers. They are used in industrial dryers, steam goes through the radiator and then air is blowed to it in order to heat the fabric. Currently my radiators are made from carbon steel tubes and fins, it has 78 flat...

I just want to ask a simple question to experts here. Can superheating of steam increases efficiency and output of thermal power plants?

Homework Statement A Carnot engine operates between 230°C and 120°C, absorbing 6.30*10^4 J per cycle at the higher temperature. What is the efficiency of the engine? Homework Equations eff = 1 - (Tcold/Thot) The Attempt at a Solution Using this equation, I get 47.83 percent...

Lets say I have a hammer, and a piece of piezoelectric quartz. If I hit the quartz with the hammer with the kinetic energy of 100 joules, how many joules can I get out of the quartz?

Sorry I was unsure where to submit this thread. I am doing a school project on designing a solar system for my home and I was wondering how the efficiency of a cell is calculated. The way I calculated it, which i read of a website is... 1. calculate area of cell (in meters) 2. divide watt...

Hi, I have a problem with determining the probability distribution function of the number n of detector counts in a given time t. I am assuming the events follow exponential distribution ε(t,λ) = λexp(-λt). Now if that was everything it would simply be a Poisson distribution, however, what I...

So, I've read in books and on Wikipedia (see for instance http://en.wikipedia.org/wiki/Carnot%27s_theorem_%28thermodynamics%29#Applicability_to_fuel_cells_and_batteries) that the Carnot efficiency cannot be applied to a fuel cell because it is not a heat engine that produces work, operating...

A secondary textbook said that if there is no flux leakage, Vp/Vs=Np/Ns, no matter what is the efficiency of the transformer. May I know will the ohmic loss and eddy current contribute to the loss and modify the voltage ratio? thanks!

Homework Statement Hey physicists. I have a problem. My assignment this term for physics is to test the efficiency of an electrical appliance, and to make suggestions on how to improve the efficiency for the future. I conducted a number of experiments on the kettle, using 2 different kettles...

While programming to find the largest prime factor for a composite number i came across a problem that if the number taken as input exceeds a certain limit, the loop time turns out to be a very long one and some times even resembling the time taken by an infinite loop.The method used for finding...

Hi all Working through a past paper as I have an exam tomorrow and can't quite see where to start with the following question. Homework Statement A steam engine produces 2.4 kJ of work per cycle for a heat input of 6 kJ. If the temperature of the hot source for the engine is 600 °C and...

Homework Statement A heat engine has a carnot efficiency of 0.11. How much internal energy does this engine use in order to do 5.1 x 10^4 joules of work? How much heat does this engine give off/exhaust?Homework Equations (change in)U=Q-W W=(change in)E

1. Determine the percent efficiency of the system www.imageshack.us/photo/my-images/818/photokt.jpg2. Ek=\frac{mv^2}{2} Eg=mgh W=FΔd W=ΔE 3. I am assuming energy is lost in this system due to friction possibly. Also assuming gravity is 9.81m/s^2 The mass of the the suspended object will be...

Homework Statement A lift motor is 70% efficient. It dose 450 000j of work lifting a load to the top floor of a building. Homework Equations What electrical energy input is required to do this? The Attempt at a Solution I first did output/input * 100 I transposed the formulae...

Homework Statement A heat engine using 110g of helium as the working substance follows the cycle shown in the figure. http://session.masteringphysics.com/problemAsset/1074114/5/19.P59.jpg What is the engine's thermal efficiency? Homework Equations n=W/Q_h The Attempt at a...

Homework Statement A heat engine is taking identical amounts of heat from two hot reservoirs at temperatures ##T_{H1}, T_{H2} ## doing work and then heat to a cold reservoir ##T_C ## What is the maximum efficiency of this heat engine? Homework Equations For a Carnot cyle it is ## \eta = 1 -...

"Jump Efficiency Theory". I am young so please no mocking. This is a theory i have created that judges how efficient a jump is with respect to a specific distance. This theory is going to be used mainly for the Long Jump sport. For example let's say you have to jump across a whole with a...

Homework Statement A step-down transformer going from 240 V to 12 V is 95% efficient. The input current is 20 A. a) Determine the primary turns: secondary turns ratio necessary in order to maintain a 12V output. b) Determine the output current. I have solved it as if I needed an secondary...

In a heat engine we ultimately care about the efficiency of the entire cycle. That is, what percentage of the heat which flows into your system is converted to work. However, you could certainly ask that same question for an individual step in a cycle. Specifically, determine the efficiency of an...

Homework Statement A boiler is to produce 6250 kg/h of steam superheated by 40 oC at a pressure of 2.1 MN/m2. The temperature of the feedwater is 50 oC. If the thermal efficiency of the boiler is 70%, how much fuel oil will be consumed in one hour? The calorific value of the fuel oil used is...

Carnot engine efficiency is: \eta_{work} = 1 - \frac{T_c}{T_h} Carnot refrigeration efficiency is: \eta_{cool} = \frac{ T_c }{T_h-T_c} \eta_{cool} = \frac{ 1 }{\frac{T_h}{T_c} - 1} Simple multiplication should give me the efficiency where both the engine and the refrigeration share the...

Homework Statement Calculate the efficiency of the heat machine that is shown in the figure. Draw the corresponding Carnot cycle diagram in the S-T plane. Homework Equations \varepsilon = \frac{ \Delta W}{\Delta Q}. \Delta Q = T \Delta S The Attempt at a Solution My problem lies in...

1. Homework Statement given: diesel cycle, P1V1 P2V2 P3V3 P4V4 - all known T1 = 20°c specific heat capacity constant pressure = 1000j/kgk specific gas constant = 287j/kgk compression index = 1.4 2. Homework Equations heres where i am stuck! 3. The Attempt at a Solution Hi...

Homework Statement Calculate the velocity ratio of the system. Third Class Lever Efficiency = 65% Mechanical Advantage = 1/6 Work Put In 3000J (I know if the system was theoretically 100% efficient the velocity ratio is 1/6 or 0.167) Homework Equations Velocity Ratio =...

In my thermodynamics class we're talking about heat pumps (i.e. refrigerators and such). When talking about a typical heat engine (carnot or not) it makes sense to me to talk about the efficiency of the engine η=1-\frac{Q_{l}}{Q_{h}}, because it clearly represents how much bang you get for you...

I have some trouble understanding the carnot cycle and why you have to make it so complicated, i.e. this process involves 2 isothermal and 2 adiabatic processes. If you want an engine with maximum efficiency why can't you just have a system whose temperature is just a tiny inch above your hot...

Can one do anything to sort of rewire the brain, so to speak. For instance, say I continually teach myself new subjects all the time. Not multitasking- just sort of "hey i learned ___, now i can teach myself ___". Can my brain get better at learning? By better I mean more efficiently.

Okay, so I have a simple D cell battery, enamel coated copper wire loop and a magnet. I can easily get the copper wire loop to spin if I scratch away part of the enamel (that side which touches the stand) off the ends of the wire, run current through a stand, and position the magnet at just the...